selftests/net/openvswitch: guard command substitutions against empty output

When ip-link output is unavailable, when the upcall daemon log has not
been written yet, or when pahole does not know the OVS drop subsystem
ID, the affected command substitutions silently produce empty strings.
The caller then passes empty sha= or pid= arguments to ovs_add_flow,
or matches against wrong drop reason codes, all without a diagnostic.

Add [ -z ] guards immediately after each assignment. For test_arp_ping,
also align the MAC extraction to use awk '/link\/ether/' as in
test_pop_vlan. The drop_reason guard returns ksft_skip because an
absent subsystem ID is an environment issue, not a test failure.

Signed-off-by: Minxi Hou <houminxi@gmail.com>
Reviewed-by: Aaron Conole <aconole@redhat.com>
Link: https://patch.msgid.link/20260604163016.3929371-1-houminxi@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

0 files changed, 0 insertions, 0 deletions